Efficient rank and precoding matrix feedback for mimo systems

ABSTRACT

The present disclosure provides a receiver, a transmitter and methods of operating a receiver or a transmitter. In one embodiment, the receiver includes a receive unit configured to receive transmissions from multiple antennas. The receiver also includes a rank feedback unit configured to feed back a transmission rank selection, wherein the transmission rank selection corresponds to a transmission rank feedback reduction scheme. The receiver further includes a preceding feedback unit configured to feed back a preceding matrix selection, wherein the preceding matrix selection corresponds to a preceding matrix feedback reduction scheme.

CROSS -REFERENCE TO PROVISIONAL APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/948,841 entitled “Efficient Rank and Precoding Matrix Feedback forSU-MIMO” to Runhua Chen, Eko N. Onggosanusi, Badri Varadarajan and AnandG. Dabak, filed on Jul. 10, 2007, which is incorporated herein byreference in its entirety.

This application also claims the benefit of U.S. Provisional ApplicationNo. 61/030,308 entitled “Efficient Rank and Precoding Matrix Feedbackfor SU-MIMO” to Runhua Chen, Eko N. Onggosanusi, Badri Varadarajan andAnand G. Dabak, filed on Feb. 28, 2008, which is incorporated herein byreference in its entirety.

TECHNICAL FIELD

The present disclosure is directed, in general, to communication systemsand, more specifically, to a receiver, a transmitter and methods ofoperating a receiver or a transmitter.

BACKGROUND

In orthogonal frequency division multiple access (OFDMA) communicationsystems, the total bandwidth is divided into non-overlapping frequencyblocks also called resource blocks (RBs), where transmissions for userequipment (UE) occur in an orthogonal and not mutually interferingmanner. Each RB carries data for a specific UE. By scheduling each UE onRBs where it has a high signal to interference and noise ratio (SINR),the data rate may be maximized according to a specific schedulingcriterion. To enable frequency-domain scheduling and allocate UEs on RBswith good SINR, each UE feeds back a channel quality indicator (CQI) toits serving base station (Node B).

For MIMO communication with downlink precoding, a pre-defined codebookis designed offline and known at the Node B and UE. The codebookconsists of a set of matrices Uε C^(N×R), where N is the number oftransmit antennas and R is the transmission rank that determines thenumber of data layers multiplexed in the spatial domain. Both thetransmission rank R and the preceding matrix U may be chosen to optimizeperformance on each RB. However, in many practical systems such as 3GPPLTE, the transmission rank R is fixed on all RBs for a given UE. Thepreceding matrix, however, could vary from one RB to the other, even forthe same UE.

In order to find an optimum rank and preceding matrix, a UE applies theestimated CQI to exhaustively search all ranks and all precedingmatrices in each rank codebook. A preferred transmission rank R andpreceding matrix U are chosen to optimize a certain optimality metricsuch as the transmission throughput according to the specific schedulingcriterion. The preferred rank and preceding matrix index are then fedback or reported to the Node B. Improvements in the selection and feedback of rank and preceding requirements would prove beneficial in theart.

SUMMARY

Embodiments of the present disclosure provide a receiver, a transmitterand methods of operating a receiver or a transmitter. In one embodiment,the receiver includes a receive unit configured to receive transmissionsfrom multiple antennas. The receiver also includes a rank feedback unitconfigured to feed back a transmission rank selection, wherein thetransmission rank selection corresponds to a transmission rank feedbackreduction scheme. The receiver further includes a preceding feedbackunit configured to feed back a preceding matrix selection, wherein thepreceding matrix selection corresponds to a preceding matrix feedbackreduction scheme.

In one embodiment, the transmitter includes a rank decoding unitconfigured to extract a transmission rank selection, wherein thetransmission rank selection corresponds to a transmission rank feedbackreduction scheme. The transmitter also includes a preceding decodingunit configured to extract a preceding matrix selection, wherein thepreceding matrix selection corresponds to a preceding matrix feedbackreduction scheme. The transmitter further includes a transmit unit thatis coupled to multiple antennas and configured to apply the transmissionrank and preceding matrix selections to data to be transmitted.

In another aspect, the method of operating a receiver includes receivingtransmissions from multiple antennas and providing a transmission rankselection, wherein the transmission rank selection corresponds to atransmission rank feedback reduction scheme. The method also includesproviding a preceding matrix selection, wherein the preceding matrixselection corresponds to a preceding matrix feedback reduction scheme.

In yet another aspect the method of operating a transmitter includesextracting a transmission rank selection, wherein the transmission rankselection corresponds to a transmission rank feedback reduction scheme.The method also includes extracting a preceding matrix selection,wherein the preceding matrix selection corresponds to a preceding matrixfeedback reduction scheme and applying the transmission rank andpreceding matrix selections to data to be transmitted.

The foregoing has outlined preferred and alternative features of thepresent disclosure so that those skilled in the art may betterunderstand the detailed description of the disclosure that follows.Additional features of the disclosure will be described hereinafter thatform the subject of the claims of the disclosure. Those skilled in theart will appreciate that they can readily use the disclosed conceptionand specific embodiment as a basis for designing or modifying otherstructures for carrying out the same purposes of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, referenceis now made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1A illustrates a system diagram of a receiver as provided by oneembodiment of the disclosure;

FIG. 1B illustrates a system diagram of a transmitter as provided by oneembodiment of the present disclosure;

FIG. 2 illustrates a diagram of an embodiment of a transmission ranksubset configuration 200 based on a receiver geometry;

FIG. 3 illustrates a flow diagram of an embodiment of a method ofoperating a receiver carried out according to the principles of thepresent disclosure;

FIG. 4 illustrates a flow diagram of an embodiment of a method ofoperating a transmitter carried out according to the principles of thepresent disclosure.

DETAILED DESCRIPTION

Rank adaptation may be allowed in the frequency domain where differentRBs choose different transmission ranks (i.e., a different number oftransmission layers). Another alternative is to perform rank adaptationonly in the time domain. In other words, the transmission rank for eachUE may be fixed across the system bandwidth at a particular point intime, because a performance gain of allowing rank adaptation in thefrequency domain may be marginal.

On the other hand, preceding matrix adaptation may be performedaccording to one of the following principles. A single widebandpreceding matrix (or its index (PMI)) may be selected for the systembandwidth. Alternatively, a single frequency-selective PMI may be chosenfor a specific frequency sub-band that includes several RBs.Furthermore, a combination of the wideband PMI in addition to thefrequency-selective sub-band PMI may also be feed back.

Since preceding adapts to an instantaneous change in the channel, thepreferred preceding matrix varies at the same feedback rate as the CQIand therefore may be assigned the same CQI feedback rate. However, thepreferred rank may change at a slower rate thereby significantlyreducing the rank feedback rate and producing a small throughput loss.Since the preferred rate for a rank feedback requirement may besubstantially different from that of preceding feedback, the rankfeedback may be defined and encoded separately from the precedingfeedback and CQI feedback.

In embodiments of this disclosure, several more efficient rank and PMIfeedback schemes are presented. The premises of these areas includesignificantly reducing the uplink feedback overhead and reducing thecomputational complexity in deriving a preferred rank and PMI.Throughout this disclosure, R(t) and P(t) may be used to denote thepreferred rank and PMI at time t.

FIG. 1A illustrates a system diagram of a receiver 100 as provided byone embodiment of the disclosure. In the illustrated embodiment, thereceiver 100 operates in an OFDMA communications system. The receiver100 includes a receive unit 105 and a feedback generator 110. Thereceive unit 105 includes an OFDM module 107 having Q OFDM demodulatorsthat are coupled to corresponding receive antennas, a MIMO detectormodule 107, a QAM demodulator, deinterleaver and FEC decoding module108, and a channel estimation module 109.

The receive unit 105 is primarily employed to receive data signals froma transmission corresponding to a transmission rank and preceding matrixselection that was determined by the receiver 100. The OFDM module 106demodulates the received data signals and provides them to the MIMOdetector 107, which employs channel estimation and precoder informationto further provide the received data to the module 108 for furtherprocessing (namely, QAM demodulation, deinterleaving, and FEC decoding).The channel estimation module 109 employs previously transmitted channelestimation signals to provide the channel estimates need by the receiver100.

The feedback generator 110 includes a CQI computer 111, a rank feedbackunit 112, a preceding feedback unit 113 and a feedback encoder 114. TheCQI computer 111 provides a channel quality based on channel estimation.The rank feedback unit 112 is configured to provide a transmission rankselection, wherein the transmission rank selection corresponds to areduction in transmission rank feedback. Correspondingly, the precedingfeedback unit 113 is configured to provide a preceding matrix selection,wherein the preceding matrix selection corresponds to a reduction inpreceding matrix feedback. The feedback encoder 114 then encodes CQIinformation, the transmission rank selection and the preceding matrixselection and feeds it back for a subsequent data transmission.

FIG. 1B illustrates a system diagram of a transmitter 150 as provided byone embodiment of the present disclosure. In the illustrated embodiment,the transmitter operates in an OFDMA communication system. Thetransmitter 150 includes a transmit unit 155 and a feedback decoder 160.The transmit unit 155 includes a modulation and coding scheme (MCS)module 156, a precoder module 157 and an OFDM module 158 having multipleOFDM modulators that feed corresponding transmit antennas. The feedbackdecoder 160 includes a feedback receiver 166, a rank decoding unit 167and a preceding decoding unit 168.

The feedback receiver 166 receives CQI information as well astransmission rank selection and preceding matrix selections that havebeen fed back. The rank decoding unit 167 is configured to extract atransmission rank selection, wherein the transmission rank selectioncorresponds to a reduction in transmission rank feedback.Correspondingly, the preceding decoding unit 168 is configured toextract a preceding matrix selection, wherein the preceding matrixselection corresponds to a reduction in preceding matrix feedback. Thetransmission rank selection is provided to the MCS module 156, and thepreceding matrix selection is provided to the precoder module 157.

Generally, the transmit unit 155 is coupled to multiple antennas andconfigured to apply the transmission rank and preceding matrixselections to data to be transmitted. The MCS module 156 and precodermodule 157 employ transmission rank and preceding matrix selectionsobtained from the feedback decoder 160. The MCS module 156 employs thetransmission rank selection to map input data to indicated spatialstreams. The precoder module 157 then maps the spatial streams linearlyinto output data streams for transmission by the OFDM module 158.

With continued reference to the receiver 100 and the transmitter 150 ofFIGS. 1A and 1B, subsequent discussions are provided for embodiments ofthe present disclosure wherein the receiver 100 is associated with userequipment (UE) and the transmitter 150 is associated with a serving basestation (Node B) in a cellular communications network. Of course, thisis only one of many embodiments based on the principles of the presentdisclosure. Some observations regarding transmission rank and precedingmatrix adaptation rates are presented in the following.

Rank adaptation occurs more frequently at higher UE speed and thereforerequires more feedback to adapt to the channel variation. When UE speedis below 10 kph, change in rank typically occurs every tens ofmilliseconds. However when the UE speed increases beyond 30 kph, thechange in rank typically occurs every five to six sub-frames, where onesub-frame is equal to one millisecond.

A dependence on receiver geometry may also be observed. In low geometryor high geometry ranges, the UE is more likely to choose the lowest orthe highest possible rank, respectively. Hence, the change intransmission rank occurs at a much lower rate. When a medium geometryrange is observed, the optimum rank may fall into a wider range ofpossible numbers (e.g., rank 1, 2, 3, or 4), thereby necessitating morefrequent rank feedback.

The change in preceding matrices happens at a significantly higher ratethan rank adaptation. Unlike rank adaptation, preceding adaptation maybe frequent, even at high and low geometry ranges. In such cases, the UEmay likely choose the highest rank (e.g., two for 4×2 transmit-receiveantenna configurations, and four for 4×4 transmit-receive antennaconfigurations) for many channel realizations. However, the optimumpreceding matrix still varies within the same rank.

Based on the above principles, the following rank feedback reductionschemes are considered. Rank feedback interval may be designed as afunction of the UE speed. When the UE moves at a higher speed, rankfeedback should be scheduled more frequently to adapt to the fastchannel variation. When UE moves at a lower speed and the channel variesslowly, rank feedback may be carried out less frequently to reduceuplink overhear. The rank feedback rate may be semi-staticallyconfigured by the higher-layer control. Note that rank feedback rate canbe UE-specific or cell-specific.

To reduce the feedback overhead, rank feedback interval may also takeinto account the UE geometry. At very low or very high geometry ranges,it is statistically more likely for the UE to persist to the lowest orthe highest rank(s) for most of the time, therefore less frequent rankfeedback may be scheduled. In the medium geometry range, the preferredrank varies within a wide range of possible ranks. Hence, feedback maybe scheduled more frequently to adapt to a faster channel variation.

Additionally, it is not precluded to configure the rank feedbackinterval by taking into account the rate of variation of interference aswell as the desired UE's channel itself. A low-speed UE may also haverapid CQI variation because of “burstiness” in neighbor cell traffic. Inthis case, a faster feedback rate may be configured for a low-speed UE.

The rank feedback interval may be configured to be larger or at least nosmaller than the CQI/PMI feedback interval. In other words, the rankfeedback rate is equal to or smaller than that of the CQI/PMI feedbackrate. Particularly, it is possible to configure the rank feedbackperiodicity to be M times larger than the CQI/PMI feedback periodicity,where M≧1. Note that the value of M may be determined at the Node B orthe UE, UE-specifically or cell-specifically. In addition, it is notprecluded to configure the rank and CQI/PMI feedback to be allowed tooccur at the same feedback instant, or forbid them to occur at the sametime by properly choosing the feedback instant.

An additional rank feedback reduction principle is given as follows. Thepreferred rank, equivalent to the number of data sub-streams transmittedsimultaneously, is chosen to maximize system performance (e.g.,throughput under a tolerated error rate). It can be considered as aprojection or mapping of a non-precoded MIMO channel into the discretespace containing all positive integer rank candidates Z={1,2,3, . . . }.Since the channel is continuous in the time domain and the preferredrank is a function of the channel, the preferred rank may also possesssome continuous-like properties in the discrete space and is thereforeunlikely to change abruptly. The preferred ranks of two consecutivefeedback instants should be close to each other. In most cases, the rankmay remain the same, increase by one or decrease by one compared to thepreferred rank of the previous feedback.

As a result of the continuous-like property, the following scheme canalso be used to reduce the feedback overhead and also reduce the ranksearch complexity. In contrast to full rank adaptation where thepreferred rank is selected from all possible ranks, it is possible toperform rank adaptation within a smaller rank subset which contains onlya few possible ranks. For example, for a 4×4 MIMO system where the fullrank set includes rank-1, rank-2, rank-3 and rank-4, the possible ranksubset could includes N different elements from {1,2,3,4} where 1≦N≦4.One example of the rank subset is {1,2}. Another example of the possiblerank subset is {3,4}.

The rank subset may be configured based on one or several parametersreflecting the overall channel condition of the UE. Examples of suchparameters include but are not limited to, geometry, condition number ofthe MIMO channel, throughput averaged over a certain window in the timedomain or frequency domain. For example, if the UE's geometry is under apre-defined lower threshold (which could be designed offline), if theUE's distance to the serving Node B is larger than a threshold or the UEis experiencing a less favorable channel and hence more likely to beoperating at a low rank.

Thus, it may be beneficial to restrict the rank adaptation within asmall rank subset (e.g., {1} or {1,2}) to reduce the rank/PMI adaptationcomplexity. On the other hand, if the UE's geometry is beyond apre-defined threshold or if its distance to the serving Node B is small,it has a better wireless channel and thus more likely to choose a higherrank. In such a case the rank subset may consist of a higher value rankcandidate (e.g., {3}, {4} or {3,4}).

FIG. 2 illustrates a diagram of an embodiment of a transmission ranksubset configuration 200 based on a receiver geometry in combinationwith other schemes. In FIG. 2, low, medium and high receiver geometryranges (LGR, MGR, HGR) are defined within a communication cell 205 forfirst and second UEs (UE1, UE2) with respect to a serving Node B. UE1may be assigned a small rank subset since it is in the low geometryrange. Correspondingly, UE2 may be assigned a high rank subset it is inthe high geometry range.

Returning to FIGS. 1A and 1B, the geometry metric used in the aboveprincipals may be calculated according to several criteria. Possiblecandidates are time average of the following parameters, (1) Frobeniusnorm of the un-precoded MIMO channel and (2) sum CQI over multiple datasub-streams. Rank subset configuration may be UE-specific,cell-specific, geometry-specific, Doppler-specific, or a combination ofthe above. The subset may be determined at the UE or configured at theNode B and sent to the UE via higher layer signaling.

Yet another rank feedback reduction scheme is possible as a result ofthe continuous-like property of rank variation. The preferred rank of aUE at a particular feedback instant may be searched over a small subsetof ranks centered around a reference rank, which may be the preferredrank of a previous feedback instant. For example denote the preferredrank at feedback instant t as R(t). Then, it is possible to searchR(t+n),n

n_(max) only from the subset

Π={R∥R−R(t)|

d _(thresh)}  (1)

where d_(thresh) bounds the maximum rank change from a previouspreferred rank feedback, and n_(max) is an integer number. It is notedthat n_(max) may be configured based on the UE speed or equivalentlyDoppler of the channel. This scheme has the benefits of reducing therank and PMI search complexity at the UE because (1) a smaller subset ofranks are searched over; and (2) only preceding matrices in the codebookof the allowed ranks are searched.

For differential rank feedback, a 1-bit feedback may be used to sendNode B the difference between the current rank and the previous rank,instead of feeding back the exact rank of the current time instant. Thepreferred rank R(t+n) is highly likely be in the set{R(t)−1,R(t),R(t)+1}. Hence, a single bit is used to denote thedifference ΔR=R(t+n)−R(t). This effectively reduces the number of bitsfor feeding back

$\begin{matrix}{{Feedback} = \left\{ \begin{matrix}1 & {{R\left( {t + n} \right)} = {{R(t)} + 1}} \\0 & {{{if}\mspace{14mu} {R\left( {t + n} \right)}} = {R(t)}} \\{- 1} & {{R\left( {t + n} \right)} = {{R(t)} - 1}}\end{matrix} \right.} & (2)\end{matrix}$

For the case of differential rank feedback, a potential issue is that oferror propagation. More precisely, when the UE's preferred rank signalis incorrectly decoded by the Node B, the Node B picks a rank that isnot what the UE has fed back. From the time the first decoding erroroccurs, the UE and the Node-B have different “local” versions of thetransmission rank. Since the feedback signaling only accounts fordifferences from the “local” transmission rank at the UE, the UE'spreferred rank and the Node B's reconstruction of the rank signal mayprogressively diverge from the time of the first error. There are twosolutions to this problem.

Signal the offset between the preferred rank of the current feedbackwith respect to the rank that has been used by the Node B, instead ofwhat the UE has chosen as the preferred rank. By doing so, when an erroroccurs in the rank feedback, the UE can move the solution graduallytowards the correct one. An alternative solution is to periodicallyreset the progression by feeding back the exact preferred rank (withoutsubset restrictions) every L milliseconds.

For preceding matrix or PMI feedback reduction schemes, the previousprinciple of choosing the preferred rank within a subset of rankcandidates close to the preferred rank of the last feedback may also beapplied to the PMI selection and feedback. A single PMI is chosen for afrequency sub-band, which contains a number of adjacent RBs, to maximizethe system throughput, which could be closely approximated as

$\begin{matrix}{T = {{\log_{2}{\det\left( {I + {\frac{\rho}{N\; \beta}{HUU}^{+}H^{+}}} \right)}} \leq {\log_{2}{\det\left( {{+ \frac{\rho}{N\; \beta}}{{HU}}_{F}^{2}} \right)}}}} & (3)\end{matrix}$

where β is the SNR gap indicating the difference between the Shannoncapacity and the actual throughput with finite MCS, and ∥(•)∥_(F) ² isthe Frobenius norm.

Conventionally, the preferred preceding matrix is chosen from the entirecodebook of all ranks based on a certain optimality metric such asthroughput maximization. However, the feedback efficiency of the art canbe improved by exploiting the channel correlation across adjacent timeinstants. More precisely, since the channel H varies smoothly over timeone expects as a result, an efficient PMI searching scheme that searchesover a subset of preceding matrices centered at the PMI of the previousfeedback. An exemplary distance measure is the Chordal distance

$\begin{matrix}{{d\left( {U_{i},U_{j}} \right)} = {\frac{1}{\sqrt{2}}{{{U_{i}U_{i}^{+}} - {U_{j}U_{j}^{+}}}}_{F}}} & (4)\end{matrix}$

Note that other distance measures are certainly not precluded. Given acertain distance measure, the preferred PMI of a given sub-band is thenselected from those matrices that are close to the preceding matrix atthe previous feedback instant. For example, one possible PMI subsetselection scheme is to search

$\begin{matrix}{{{U\left( {t + n} \right)} = {\underset{{U{({t + n})}} \in \Psi}{\text{arg}\max}\log_{2}\text{det}\left( {I + {\frac{\rho}{N\; \beta}{HUU}^{+}H^{+}}} \right)}},{n \leq n_{\max}}} & (5)\end{matrix}$

where

Ψ={U|d(U,U(t))

Γ}  (6)

is the subset of precoding matrices whose distance to the previouspreceding matrix is bounded by a threshold Γ. As a small subset of thecodebook is searched over, the selection or computational complexity andthe number of bits for PMI feedback are both reduced.

Alternatively, it is also feasible to search the preferred PMI for eachsub-band from a subset of PMIs whose distance to the wideband PMI of thecurrent or a previous feedback instant is within a given threshold. Thewideband PMI is a single PMI selected for the system bandwidth or afraction of the system bandwidth configured for the wideband PMIselection. The threshold for PMI subset restriction could be UEspecific, cell specific or configured at either the UE or the Node B.

Note that the codebook is pre-defined and a distance metric between twoarbitrary precoding matrices is known. Therefore, defining a distancethreshold is equivalent to defining the size of the preceding matrixsubset to search over. In other words, the size of the candidate matrixsubset N (e.g., 2,4,6,8, etc.) may be defined, which is the number ofthe closest precoding matrices to the previous preceding matrix that wasfed back.

An adaptive PMI may be fed back (similar to the rank in a differentialformat) to reduce the feedback rate, where the differential is takenover the index of the PMI matrices. Techniques analogous to thedifferential rank feedback may be used to mitigate error propagation indifferential PMI feedback.

FIG. 3 illustrates a flow diagram of an embodiment of a method 300 ofoperating a receiver carried out according to the principles of thepresent disclosure. The method 300 starts in a step 305 andtransmissions from multiple antennas are received in a step 310. Then,in a step 315, a transmission rank selection is fed back, wherein thetransmission rank selection corresponds to a transmission rank feedbackreduction scheme.

In one embodiment, an update rate of the transmission rank selection isa function of a speed of the receiver. Additionally, the transmissionrank selection is based on a receiver geometry with respect to themultiple antennas that provide the transmissions. Correspondingly, thetransmission rank selection is restricted to a subset of availabletransmission ranks that is either determined by the receiver orconfigured by the received transmissions.

In one embodiment, the transmission rank selection is a differentialrank that corresponds to a difference between a current transmissionrank and a reference transmission rank. Additionally, the referencetransmission rank may include the last transmission rank selection.

A preceding matrix selection is fed back, wherein the preceding matrixselection corresponds to a preceding matrix feedback reduction scheme,in a step 320. In one embodiment, the preceding matrix selectioncorresponds to a single preceding matrix for a frequency sub-band thatcontains at least two adjacent resource blocks. Alternatively, thepreceding matrix selection is restricted to a subset of availablepreceding matrices that is also determined by the receiver or configuredby the received transmissions.

In one embodiment, the precoding matrix selection is a differentialpreceding matrix that corresponds to a difference between a currentpreceding matrix and a reference preceding matrix. The preceding matrixselection may correspond to a time domain representation or a frequencydomain representation.

In one embodiment, the preceding matrix selection corresponds to asubset of precoding matrices that relates to a reference precedingmatrix, and the reference preceding matrix is the last preceding matrixselection. Alternatively, the reference preceding matrix may be awideband preceding matrix selected for at least a portion of the systembandwidth. Additionally, the subset may contain preceding matrices thatare closest to the reference preceding matrix according to a distancemeasure wherein the distance measure is selected employing a Chordaldistance norm or a Frobenius distance norm. The method 300 ends in astep 325.

FIG. 4 illustrates a flow diagram of an embodiment of a method 400 ofoperating a transmitter carried out according to the principles of thepresent disclosure. The method 400 starts in a step 405. Then, in a step410, a transmission rank selection is extracted, wherein thetransmission rank selection corresponds to a transmission rank feedbackreduction scheme.

In one embodiment, an update rate of the transmission rank selection isa function of a speed of a receiver. Additionally, the transmission rankselection is based on a receiver geometry with respect to multipletransmit antennas. Correspondingly, the transmission rank selection isrestricted to a subset of available transmission ranks that isconfigured by the transmitter or determined by a receiver.

In one embodiment, the transmission rank selection is a differentialrank that corresponds to a difference between a current transmissionrank and a reference transmission rank. Additionally, the referencetransmission rank may include the last transmission rank selection.

In a step 415, a preceding matrix selection is extracted, wherein thepreceding matrix selection corresponds to a preceding matrix feedbackreduction scheme. In one embodiment, the preceding matrix selectioncorresponds to a single preceding matrix for a frequency sub-band thatcontains at least two adjacent resource blocks. Alternatively, thepreceding matrix selection is restricted to a subset of availablepreceding matrices that is also configured by the transmitter ordetermined by a receiver.

In one embodiment, the preceding matrix selection is a differentialpreceding matrix that corresponds to a difference between a currentpreceding matrix and a reference preceding matrix. The preceding matrixselection may correspond to a time domain representation or a frequencydomain representation.

In one embodiment, the preceding matrix selection corresponds to asubset of preceding matrices that relates to a reference precedingmatrix wherein the reference preceding matrix may be the last precedingmatrix selection. Alternatively, the reference preceding matrix is awideband preceding matrix selected for at least a portion of the systembandwidth. Additionally, the subset contains precoding matrices that areclosest to the reference preceding matrix according to a distancemeasure, wherein the distance measure is selected employing a Chordaldistance norm or a Frobenius distance norm. The transmission rank andpreceding matrix selections are applied to data to be transmitted in astep 420, and the method 400 ends in a step 425.

While the methods disclosed herein have been described and shown withreference to particular steps performed in a particular order, it willbe understood that these steps may be combined, subdivided, or reorderedto form an equivalent method without departing from the teachings of thepresent disclosure. Accordingly, unless specifically indicated herein,the order or the grouping of the steps is not a limitation of thepresent disclosure.

Those skilled in the art to which the disclosure relates will appreciatethat other and further additions, deletions, substitutions andmodifications may be made to the described example embodiments withoutdeparting from the disclosure.

1. A receiver, comprising: a receive unit configured to receivetransmissions from multiple antennas; a rank feedback unit configured toprovide a transmission rank selection, wherein the transmission rankselection corresponds to a transmission rank feedback reduction scheme;and a preceding feedback unit configured to provide a preceding matrixselection, wherein the preceding matrix selection corresponds to apreceding matrix feedback reduction scheme.
 2. The receiver as recitedin claim 1 wherein an update rate of the transmission rank selection isa function of a receiver speed.
 3. The receiver as recited in claim 1wherein the transmission rank selection is based on a receiver geometry.4. The receiver as recited in claim 1 wherein the transmission rankselection is restricted to a subset of available transmission ranks thatis transmission-configured or receiver-determined.
 5. The receiver asrecited in claim 1 wherein the transmission rank selection is adifferential rank that corresponds to a difference between a currenttransmission rank and a reference transmission rank.
 6. The receiver asrecited in claim 5 wherein the reference transmission rank includes thelast transmission rank selection.
 7. The receiver as recited in claim 1wherein the preceding matrix selection corresponds to a single precedingmatrix for a frequency sub-band that contains at least two adjacentresource blocks.
 8. The receiver as recited in claim 1 wherein thepreceding matrix selection is restricted to a subset of availablepreceding matrices that is transmission-configured orreceiver-determined.
 9. The receiver as recited in claim 1 wherein thepreceding matrix selection corresponds to a subset of preceding matricesthat relates to a reference preceding matrix.
 10. The receiver asrecited in claim 9 wherein the reference preceding matrix is the lastpreceding matrix selection.
 11. The receiver as recited in claim 9wherein the reference preceding matrix is a wideband preceding matrixselected for at least a portion of the system bandwidth.
 12. Thereceiver as recited in claim 9 wherein the subset contains precedingmatrices that are closest to the reference preceding matrix according toa distance measure.
 13. The receiver as recited in claim 12 wherein thedistance measure is selected from the group consisting of: a Chordaldistance norm; and a Frobenius distance norm.
 14. The receiver asrecited in claim 1 wherein the preceding matrix selection is adifferential preceding matrix that corresponds to a difference between acurrent preceding matrix and a reference preceding matrix.
 15. Thereceiver as recited in claim 1 wherein the precoding matrix selectioncorresponds to a time domain representation or a frequency domainrepresentation.
 16. A method of operating a receiver, comprising:receiving transmissions from multiple antennas; feeding back atransmission rank selection, wherein the transmission rank selectioncorresponds to a transmission rank feedback reduction scheme; andfeeding back a preceding matrix selection, wherein the precoding matrixselection corresponds to a preceding matrix feedback reduction scheme.17. The method as recited in claim 16 wherein an update rate of thetransmission rank selection is a function of a receiver speed.
 18. Themethod as recited in claim 16 wherein the transmission rank selection isbased on a receiver geometry.
 19. The method as recited in claim 16wherein the transmission rank selection is restricted to a subset ofavailable transmission ranks that is transmission-configured orreceiver-determined.
 20. The method as recited in claim 16 wherein thetransmission rank selection is a differential rank that corresponds to adifference between a current transmission rank and a referencetransmission rank.
 21. The method as recited in claim 20 wherein thereference transmission rank includes the last transmission rankselection.
 22. The method as recited in claim 16 wherein the precedingmatrix selection corresponds to a single preceding matrix for afrequency sub-band that contains at least two adjacent resource blocks.23. The method as recited in claim 16 wherein the preceding matrixselection is restricted to a subset of available preceding matrices thatis transmission-configured or receiver-determined.
 24. The method asrecited in claim 16 wherein the preceding matrix selection correspondsto a subset of preceding matrices that relates to a reference precedingmatrix.
 25. The method as recited in claim 24 wherein the referencepreceding matrix is the last preceding matrix selection.
 26. The methodas recited in claim 24 wherein the reference preceding matrix is awideband preceding matrix selected for at least a portion of the systembandwidth.
 27. The method as recited in claim 24 wherein the subsetcontains preceding matrices that are closest to the reference precedingmatrix according to a distance measure.
 28. The method as recited inclaim 27 wherein the distance measure is selected from the groupconsisting of: a Chordal distance norm; and a Frobenius distance norm.29. The method as recited in claim 16 wherein the preceding matrixselection is a differential preceding matrix that corresponds to adifference between a current preceding matrix and a reference precedingmatrix.
 30. The method as recited in claim 16 wherein the precedingmatrix selection corresponds to a time domain representation or afrequency domain representation.
 31. A transmitter comprising: a rankdecoding unit configured to extract a transmission rank selection,wherein the transmission rank selection corresponds to a transmissionrank feedback reduction scheme; a preceding decoding unit configured toextract a preceding matrix selection, wherein the preceding matrixselection corresponds to a preceding matrix feedback reduction scheme;and a transmit unit that is coupled to multiple antennas and configuredto apply the transmission rank and preceding matrix selections to datato be transmitted.
 32. The transmitter as recited in claim 31 wherein anupdate rate of the transmission rank selection is a function of areceiver speed.
 33. The transmitter as recited in claim 31 wherein thetransmission rank selection is based on a receiver geometry.
 34. Thetransmitter as recited in claim 31 wherein the transmission rankselection is restricted to a subset of available transmission ranks thatis transmitter-configured or receiver-determined.
 35. The transmitter asrecited in claim 31 wherein the transmission rank selection is adifferential rank that corresponds to a difference between a currenttransmission rank and a reference transmission rank.
 36. The transmitteras recited in claim 35 wherein the reference transmission rank includesthe last transmission rank selection.
 37. The transmitter as recited inclaim 31 wherein the preceding matrix selection corresponds to a singlepreceding matrix for a frequency sub-band that contains at least twoadjacent resource blocks.
 38. The transmitter as recited in claim 31wherein the preceding matrix selection is restricted to a subset ofavailable preceding matrices that is transmitter-configured orreceiver-determined.
 39. The transmitter as recited in claim 31 whereinthe preceding matrix selection corresponds to a subset of precedingmatrices that relates to a reference preceding matrix.
 40. Thetransmitter as recited in claim 39 wherein the reference precedingmatrix is the last preceding matrix selection.
 41. The transmitter asrecited in claim 39 wherein the reference preceding matrix is a widebandpreceding matrix selected for at least a portion of the systembandwidth.
 42. The transmitter as recited in claim 39 wherein the subsetcontains preceding matrices that are closest to the reference precedingmatrix according to a distance measure.
 43. The transmitter as recitedin claim 42 wherein the distance measure is selected from the groupconsisting of: a Chordal distance norm; and a Frobenius distance norm.44. The transmitter as recited in claim 31 wherein the preceding matrixselection is a differential preceding matrix that corresponds to adifference between a current preceding matrix and a reference precedingmatrix.
 45. The transmitter as recited in claim 31 wherein the precedingmatrix selection corresponds to a time domain representation or afrequency domain representation.
 46. A method of operating a transmittercomprising: extracting a transmission rank selection, wherein thetransmission rank selection corresponds to a transmission rank feedbackreduction scheme; extracting a preceding matrix selection, wherein thepreceding matrix selection corresponds to a preceding matrix feedbackreduction scheme; and applying the transmission rank and precedingmatrix selections to data to be transmitted.
 47. The method as recitedin claim 46 wherein an update rate of the transmission rank selection isa function of a receiver speed.
 48. The method as recited in claim 46wherein the transmission rank selection is based on a receiver geometry.49. The method as recited in claim 46 wherein the transmission rankselection is restricted to a subset of available transmission ranks thatis transmitter-configured or receiver-determined.
 50. The method asrecited in claim 46 wherein the transmission rank selection is adifferential rank that corresponds to a difference between a currenttransmission rank and a reference transmission rank.
 51. The method asrecited in claim 50 wherein the reference transmission rank includes thelast transmission rank selection.
 52. The method as recited in claim 46wherein the preceding matrix selection corresponds to a single precedingmatrix for a frequency sub-band that contains at least two adjacentresource blocks.
 53. The method as recited in claim 46 wherein thepreceding matrix selection is restricted to a subset of availablepreceding matrices that is transmitter-configured orreceiver-determined.
 54. The method as recited in claim 46 wherein thepreceding matrix selection corresponds to a subset of preceding matricesthat relates to a reference preceding matrix.
 55. The method as recitedin claim 54 wherein the reference preceding matrix is the last precedingmatrix selection.
 56. The method as recited in claim 54 wherein thereference preceding matrix is a wideband preceding matrix selected forat least a portion of the system bandwidth.
 57. The method as recited inclaim 54 wherein the subset contains preceding matrices that are closestto the reference preceding matrix according to a distance measure. 58.The method as recited in claim 57 wherein the distance measure isselected from the group consisting of: a Chordal distance norm; and aFrobenius distance norm.
 59. The method as recited in claim 46 whereinthe preceding matrix selection is a differential preceding matrix thatcorresponds to a difference between a current preceding matrix and areference preceding matrix.
 60. The method as recited in claim 46wherein the preceding matrix selection corresponds to a time domainrepresentation or a frequency domain representation.